Does one liter of any fluid equal one kg?

Answer 1

For water 1 kg = 1 liter. For anything else, you will need to know the density of the liquid. Most things are close enough. A liter of water have a density of 1 g/cm³ and a liter of milk has a density of 1.026g/cm³ not much of a difference.
For standard water under standard conditions: 1 liter has 1 kg of mass, weighs 9.8 newtons or 2.20462 pounds on earth.

Answer 2

One litre of any fluid does not equal one kilogram. The mass of a litre of liquid will be determined by its density. The amount of molecules that are crammed into the same amount of space will determine its final mass. So there.